Conventionally, so-called compact disks (hereinafter referred to as CDs) have been widely used whereon successive information such as music information is recorded as digital signals in the form of optically detectable minute pits. Meanwhile, CD-ROMs (Compact Disc Read Only Memory), whereon discrete information such as computer-use data as well as music information is recorded, have been viewed with interest for its characteristics of large storage capacity and high productivity and already come into use (hereinafter CD-ROMs are included in CDs for convenience). Information on the CDs is reproducible through optical disk reproducing devices for only reproduction (CD players).
FIG. 10 and FIG. 11 are schematic views illustrating a signal format used in the CDs. As shown in FIG. 10, a frame 50a of a recording signal is composed of a frame synchronization signal 50b indicating a head of the frame, a sub-code 50c for additional information data, and a data field 50d having 24-byte main information data and 8-byte error detection and correction parity code added thereto.
In addition, the data field 50d is formed by an error detecting and correcting method including non-complete interleaving called CIRC (Cross Interleaved Reed Solomon Code).
As shown in FIG. 11, ninety-eight of the frame 50a form a sub-coding frame 51a (hereinafter referred to as a sector). Further, ninety-eight of the sub-code 50c in each frame 50a form a sub-coding block 51c. Information such as track numbers (corresponding to music numbers when main information is of music programs), or absolute address information on the disk is indicated by data in the sub-coding block 51c.
Since the length of each sector corresponds to 13.3 ms, seventy five sectors are equivalent to a second. In this case, sector numbers on the disk can be described base on the following data, "minute": "second": "a sector number in one second (taking a value from 00 through 74)". The sector number corresponds to successive time-indicating information and position-indicating information and consecutively increases from an innermost outward of the disk.
FIG. 12 is a typical depiction illustrating an area allocation on the CD. A disk 52 is provided with a main information recording area 52b and a TOC (Table of Contents) area 52a. The main information recording area 52b stores main information such as music information and sector numbers according to the sub-code information.
The TOC area 52a stores additional information of the sub-code relating to respective information recorded in the main information recording area 52b, such as a track number and a recording start sector number of each track. The TOC area 52a also stores other kinds of information such as distinctive information for determining whether recorded information on a track is audio information such as music information or computer-use data.
According to the format, when loading a disk into the CD player, sub-code information in the TOC area 52a is read out, then the number of main information (corresponding to the number of music programs for music information), sector numbers of recording start positions of respective information and a sort of information (whether successive information such as audio information or discrete information such as computer-use data) are recognized. Thereafter, an access operation to a desired track is promptly carried out upon receiving instructions to perform reproducing operation by collating information in the TOC area 52a with the sub-code sector numbers in the main information recording area 52b.
When recording on the CDs, a so-called CLV (Constant Linear Velocity) system is employed for a rotation control. With this system, a recording density becomes constant at any position of the disk. This characteristic is preferable for increasing recording capacity. In a CD player, the CLV control is carried out by controlling a disk rotation such that an interval of the reproduced signal, for example, the frame synchronization signal, which is recorded on the CD at CLV, becomes a reference length.
The following discusses the conventional CD player referring to FIG. 13.
The FIG. 13 is a block diagram illustrating a configuration of the CD player. A spindle motor 62 for supporting a CD disk 61 is controlled by a CLV control circuit 63 so that the CD disk 61 rotates at a constant linear velocity. Then, an optical head 64 is moved to a desired position on the CD disk 61 by means of a moving function (not shown). When a laser beam is projected on the CD disk 61 through the optical head 64, the resulting reflected light beams are converted into an electronic signal according to the intensities thereof. Further, the electronic signal is amplified by a reproduction amplifier 65. Then, it is sent as a reproduced signal to a first clock generation circuit 66 and a reproduced data processing circuit 67.
The first clock generation circuit 66 is composed of a so-called PLL (Phase Locked Loop) which generates a clock in synchronization with the reproduced signal from the reproduction amplifier 65. Further, the reproduced data processing circuit 67 distinguishes the reproduced signal by using a clock generated by the first clock generation circuit 66 and separates the frame synchronization signal therefrom. The reproduced data processing circuit 67 also demodulates "EFM" (Eight to Fourteen Modulation) modulated reproduced data. Thereafter, the CIRC is decoded by a memory 72 for the purpose of correcting errors in the reproduced signal.
A clock system for processing the reproduced data is discussed in detail hereinbelow. When writing the "EFM" demodulated reproduced data in the memory 72, a clock in synchronization with the reproduced signal is required For this reason, the clock generated by the first clock generation circuit 66 is sent to a write address generation circuit 68. A memory address in synchronization with the clock is continuously output from the write address generation circuit 68. A memory address is sent to the memory 72 via a switch 71, whereby the "EFM" demodulated data is written in the memory 72 in a determined order.
On the other hand, a second clock generation circuit 69 is provided for a read-out operation from the memory 72. The second clock generation circuit 69 generates a clock having a determined reference frequency. In a read address generation circuit 70, a memory address is generated according to the reference clock generated by the second clock generation circuit 69. The memory address is continuously sent to the memory 72 via the switch 71, whereby the data from the memory 72 is read out in a determined order. In the reading data, the main data shown in FIG. 11 is again converted into analog audio information by a D/A converter 73 and then output to a terminal 74.
In addition, the write address generation circuit 68 and the read address generation circuit 70 do not have the same address generation order. These circuits also de-interleave the data into the original order, which had been re-arranged through the interleaving method when recording on the disk.
Further, since an actual storage capacity of the memory 72 is limited, writing and read-out operations of the data in and from the memory 72 may not be performed accurately. In order to counteract this, the CLV control circuit 63 makes a fine adjustment on the spindle motor 62 such that, for example, a frequency of the frame synchronization signal in the reproduced signal becomes always a reference frequency of the second clock generation circuit 69. As a result, a successive reproducing operation can be surely performed.
Another reference clock is used for generating addresses in the read address generation circuit 70 other than the reference clock in synchronization with the reproduced signal. This contributes to absorb the deviation in the reproduced signal of the disk rotation system, thereby permitting to perform a reproducing operation with hi-fi audio without having a time based deviation. This is the advantageous characteristic of the digital audio apparatuses and normally called TBC (Time Base Correcting).
Next, a controlling process of an access operation using the CD player having the described configuration is discussed in reference to a flow chart in FIG. 14.
When instructions for reproduction are given by, for example, a user, the optical head 64 is moved to an reproduction start absolute address position on the disk as instructed (S 31 and S 32). When the optical head 64 has been moved to the address position, a still jump (a backward jump per rotation of the disk) is made so that the optical head 64 is held in a wait-state by keeping the light beam at a radial position of the disk (S 33). Then, the CLV control starts (S 34).
After waiting until the determined linear velocity is obtained (S 35), the optical head is held in another wait-state at the radial position of the disk until obtaining a target reproduction start absolute address (S 36). This normally refers to as a waiting time for a disk rotation. Upon obtaining the target reproduction start absolute address, the still jumping operation is set off (S 37), thereby starting the reproducing operation.
Next, regarding variations in the number of the disk rotations, the disk linear velocity and the reproduced signal synchronization clock thus controlled, an example is given by showing a case of accessing from an outer portion toward an inner portion of the disk referring to FIG. 15.
The disk linear velocity gradually decreases as the optical head 64 moves towards the inner portion of the disk. This is because the number of the disk rotations during the time intervals m2 and m3 are substantially the same as the number of the disk rotations during the time interval ml which ends at t1 at which the instructions for reproduction are given. The time intervals m2 and m3 are for moving the optical head. Here, the reproduced signal synchronization clock gradually decreases in response to the reproduced signal of the disk during the time interval m2 which ends at t2. During the time interval m3, it lies outside the range wherein the PLL is locked and held in a preserve state.
After the optical head has been moved to the target position, the CLV control starts at t3. From t3, both the number of disk rotations and the linear velocity gradually increase. Then, after an elapse of time intervals m4 and m5, the number of the disk rotations and the linear velocity within the determined range are obtained at t5. Meanwhile, the reproduced signal synchronization clock starts increasing from t4 as the reproduced signal increases after an elapse of the time interval m4 as a preserve period. Then, after an elapse of a time interval m6 corresponding to the waiting time for the disk rotation, the reproducing operation starts.
Thus, the discussed CLV system is time consuming in comparison with the CAV (Constant Angular Velocity) system because not only for moving the optical head and the disk rotation, waiting time is required also for the linear velocity control and for another disk rotation before starting the reproducing operation. The CAV system has been generally used when reproducing information from the conventional floppy disks or hard disks, etc., at a constant angular velocity (a constant number of rotation).
When using a re-writable disk such as a magneto-optical disk which has been recently developed, whereon various types of information such as music information, computer-use data, etc., are recorded, the information recording and reproducing device is preferably designed to be compatible with the conventional CD player by employing a common reproducing method.
In this case, especially for an initial disk whereon information has not been recorded, an access operation to sector positions prior to recording nor the CLV control which is required during recording cannot be executed. This is because the initial disk does not have absolute address information defined by the sub-code of the signal format used in the CDs nor the frame synchronization signal used in the CLV control and the like.
To counteract the above-mentioned problems, the following method is proposed as an alternative method for recording absolute addresses without using sub-code information. In this method, guiding grooves on the disk are displaced inward or outward in a radial direction after being "biphase-mark" modulated, or the widths of the guiding grooves on the disk are varied depending on the value of each bit: "0" or "1" (for example, see U.S Pat. No. 4,907,216).
In this case, if a frequency band of a "biphase-mark" modulated absolute addresses and a frequency band of "EFM" modulated recording information are set to differ, the respective reproducing operations can be performed separately. This enables access to an area even whereon no information has been recorded by using the absolute addresses associated with the guiding grooves.
Moreover, by using a reproduction carrier component of the absolute address, more concretely, by comparing the reproduction carrier component with a reference clock generated in the device, an accurate CLV control can be achieved. This is also true during the recording operation. Here, when recording information, the recording signal can be generated by coding/modulating recording information using the reference clock.
Since CDs have large storage capacity, a reproduced data processing device using the CDs described is preferably arranged such that reproducing operation can be performed by promptly accessing to a desired piece of information from the recording medium. Further, another reproduced data processing device using a re-writable disk which is compatible with the CDs, is preferably arranged such that the reproducing operation of various types of information (not restricted to music information) can be performed, especially as an information recording medium for home use by utilizing the disk's advantageous characteristic of being accessible at high speed.
However, when information is recorded using the signal format of the CDs described, an access operation is required prior to the recording operation. The access operation is for controlling the disk rotation to be the determined linear velocity after the optical head has been moved to the desired absolute address position.
In the access operation, the time required for obtaining a constant linear velocity after moving the optical head to the determined address position is generally longer than the time required for moving the optical head to the determined address position. Especially when moving from an innermost portion to a circumferential potion of the disk or vice versa, the ratio of the disk rotation speed is 2:1 or greater where the access time is maximized.
FIG. 16 shows a relationship between various operations for starting up a recording operation and the disk rotation speed in accordance with the information recording and reproducing device employing the re-writable disk. FIG. 17 is a flow chart showing a process up to when the reproducing operation starts.
In FIGS. 16 and 17, when instructions for recording are given by the host device or a user (S 0), the optical head is moved to the target recording start absolute address position as instructed (S 1). Then, it is judged whether or not the optical head has reached the target absolute address position (S 2). Here, the disk rotation speed is kept substantially constant during the time interval m2, i.e., from t1 at which the optical head starts to move until t2 at which the optical head reaches the target absolute address position.
When the optical head has reached the target absolute address position, it is held in a still and wait state by making a still jump (a backward jump by one track which the light beam makes per rotation of the disk) (S 3). In the mean time, the CLV control is enabled (S 4).
Then, it is judged whether or not the determined linear velocity has been obtained (S 5). After an elapse of a time interval m3, if the linear velocity has the predetermined value at t3, it is next to be judged whether or not the optical head has reached the target absolute address position within the track from which the reproducing operation is repeatedly performed by making a still jump (S 6).
After an elapse of a time interval m4, if the optical head has indeed reached the target absolute address, the still jumping operation is set off (S 7), then the recording operation starts (S 8).
As is evident from the above explanation, the discussed CLV system is time consuming in comparison with the so-called CAV (Constant Angular Velocity) system because not only for moving the optical head in a radial direction and the disk rotation, waiting time is required also for the linear velocity control and for another disk rotation.
This may not cause a serious problem when recording successive information having a large memory such as music information. However, as for discrete information such as computer-use data, every time performing a recording operation, additional waiting time is required for a linear velocity control. Thus, this system is not suitable especially when information has small memory and when recording and re-writing operations are performed frequently.
Moreover, even if the driving capability for moving the optical head in a radial direction is improved for the purpose of improving the access velocity, the waiting time required for the linear velocity control and for the disk rotation until reaching the target absolute address position cannot be shortened. Thus, the problem this causes of the long access time still remains unsolved.
On the other hand, when reproducing information using the discussed conventional method, an additional waiting time is required for obtaining a determined linear velocity by controlling the number of disk rotations as well as the waiting time required for a so-called access operation, i.e., for moving the optical head to a desired position on the disk. This causes the problem that the reproducing operation cannot be performed promptly.
The waiting time for controlling the number of the disk rotations is usually longer than the time required for moving the optical head. Especially when moving from an innermost portion to a circumferential portion (or from the circumferential portion to the innermost portion) of the disk, the ratio of the disk rotation speed is 2:1 or greater where the access time is maximized. This problem is not serious when dealing with audio information like music information. However, as for discrete information such as computer-use data, every time performing a reproducing operation, additional waiting time is required for a linear velocity control. This causes the problem that the computer's capability in terms of processing is lowered.
Moreover, even if the driving capability for moving the optical head in a radial direction is improved for the purpose of improving the access velocity, the waiting time for the rotation control and for the disk rotation will override the improved driving capability, thereby failing to obtain an overall improvement in the access velocity.
FIG. 18 is a diagram for discussing another problem which arises when adopting the discussed CD format to the re-writable disk. The figure illustrates a reproducing operation when recorded information is stored in five sectors from (n) to (n+4) with respect to a sector line (see FIG. 18 (a)) on the disk having a unique absolute address value indicated by pre-recorded information such as rotation control information, etc.
Here, a reproduced signal is shown in FIG. 18 (b). Sectors other than the five sectors, i.e., a sector (n-1) and sectors (n+5) through (n+7) represent areas whereon no information has been recorded. The reproduced signal is converted into a digital reproduced signal (see FIG. 18 (c)) by means of, for example, a comparator. However, in the area whereon no information has been recorded, i.e., the sector (n-1) and the sectors (n+5) through (n+7), the reproduced signal (see FIG. 18 (b)) is in the noise level, and corresponding digital reproduced signals (c1) and (c3) become meaningless data having high frequency components.
Thus, as shown in FIG. 18 (d), in the area whereon no information has been recorded, the PLL, for generating a clock in synchronization with the reproduced signal, generates a clock having a high frequency as a result of following the digital reproduced signal (a vertical axis indicates the frequency).
Here, an explanation is given in accordance with the discussed TBC operation. A clock for memory writing (see FIG. 18 (e)) is in synchronization with the reproduced signal. Thus, in areas (e1) and (e3), information is written in a memory using a clock having a high frequency. On the other hand, a clock for memory reading out (see FIG. 18 (f)) is a reference clock having a determined frequency. Thus, there is a difference of the frequences between the clock for memory writing and the clock for memory reading out as is shown in FIG. 18 (g).
For this reason, so called memory over-flowing phenomenon occurs wherein new data is written before reading out pre-recorded data. This depends on the storage capacity of the memory. The detection of the memory over-flow is shown in FIG. 18 (h) (a memory over-flowing state is represented by a high level).
On the other hand, the sectors (n) through (n+4), i.e., the sectors for reproduction, the data stored in these sectors on the disk is reproduced and then written in the memory. Here, a determined time delay arises from de-interleaving and error correcting operations done using the CIRC. Thus, as shown in FIG. 18 (i), the memory read-out operation of the data corresponding to the sectors (n) through (n+4) is lagged and performed respectively in accordance with (d1) through (d5).
Therefore, during the read-out operation of the data (d5), memory over-flow arises at a transfer point from a low level to a high level as shown in FIG. 18 (h). Thus, a part of the data (d5) stored in the memory is destroyed, thereby presenting the problem of triggering errors.